APICAL ECTODERMAL RIDGE ACTIVITY AND JOINT FORMATION

项目1将侧重于两个基本进程的各个方面， 肢体模式形成、AER定向生长和肢体模式化 中胚层和连续软骨骨骼的分割 通过联合形成将雏形分裂成两个或多个独立的元素。许多 AER的细胞随着AER的持续凋亡而持续发生凋亡， 指导肢体的生长和形成模式，这表明编程细胞 死亡可能在维持AER活性中起重要作用， 信号装置.这一假设将通过使用AER进行部分检验- Msx-2基因中靶向异位表达的特异性增强子元件 Bcl-2，一种有效的细胞凋亡抑制剂，特别是对AER， 转基因小鼠的四肢发育，以确定是否AER指导 肢体的生长或模式被改变。Msx-2和BMP是高度 在ER中表达，并参与调节细胞凋亡。 轻中胚层，这表明Msx-2和BMPS可能是在一个调节 控制广泛的程序性细胞死亡的网络， 在AER中不断发生。研究它们在AER中的作用， 研究它们在细胞凋亡中的可能作用，以及AER特异性增强子 Msx-2基因中的元件将用于指导 BMP或Msx-2的抑制剂对转基因小鼠的AER起作用。的 含有同源框的基因Cux，果蝇Cut的鸡直系同源物 基因，是高度表达在所有的离散网站的初期 关节形成在发展肢体，是Gdf5，骨形态发生蛋白家族成员 这已被证明在关节形成中起重要作用。的 假设Cux在调节肿瘤的发生中起着至关重要的作用， 在骨骼元素之间生成关节的分割过程 的肢体将被调查，以及可能的关系， Cux和GDF5之间的联系关节形成的开始是 其特征在于分化软骨细胞的联合转化 表达大量软骨的细胞 典型的II型胶原蛋白进入扁平密集的细胞 表达很少或不表达II型胶原的关节间区。 脊椎动物切割同源物通常是转录阻遏物， 抑制多种谱系中组织特异性基因的表达。 因此，假设考克斯可能调节关节形成的开始 至少部分通过抑制II型胶原蛋白的表达 基因或其他软骨特异性基因，从而促进形成 的关节间组织，将进行研究。

Project 1 will focus on aspects of two fundamental processes involved in limb pattern formation, AER-directed outgrowth and patterning of limb mesoderm, and the segmentation of continuous cartilaginous skeletal rudiments into two or more separate elements by joint formation. Many of the cells of the AER continuously undergo apoptosis as the AER is directing limb outgrowth and patterning, suggesting that programmed cell death may play an important role in maintenance of AER activity and signalling. This hypothesis will be tested in part by using an AER- specific enhancer element in the Msx-2 gene to target ectopic expression of Bcl-2, a potent inhibitor of apoptosis, specifically to the AER of the developing limbs of transgenic mice to determine if AER directed outgrowth or patterning of the limb is altered. Msx-2 and BMPs is highly expressed in the ER and have been implicated in regulating apoptosis in light mesoderm, suggesting that Msx-2 and BMPS may be in a regulatory network that controls the extensive programmed cell death that continuously occurs in the AER. To study their functions in the AER and examine their possible roles in apoptosis, and AER-specific enhancer element in the Msx-2 gene will be used to direct the expression of inhibitors of BMP or Msx-2 function to the AERs of transgenic mice. The homeobox-containing gene Cux, the chicken ortholog of the Drosophila Cut gene, is highly expressed at all of the discrete sites of incipient joint formation in the developing limb, as is Gdf5, a BMP family member which has been shown to lay an important role in joint formation. The hypothesis that Cux plays a crucial role in regulating the onset of the segmentation process that generates joints between the skeletal elements of the limb will be investigated, as will the possible relationship between Cux and GDF5 in the process. The onset of joint formation is characterized by the joint conversion of differentiating chondrocytes that express high amounts that express high amounts of cartilage- characteristic type II collagen into the flattened densely packed cells of the joint interzone which express little or no type II collagen. Vertebrate Cut homologs in general are transcriptional repressors that inhibit the expression of tissue specific genes in multiple lineages. Thus the hypotheses that Cox might regulate the onset of joint formation at lest in part by repressing the expression of the type II collagen gene or other cartilage specific genes, thus facilitating the formation of the joint interzone tissue, will be studied.